Direct current (DC) converters are known. Such devices have usefulness wherever power of differing voltages are needed for devices having differing requirements in the same or closely related systems. For example, a processor chip of a personal computer may require power at a very low level (i.e., 5 volts or less) while a hard disk drive may require power at a much higher level (i.e., 12 volts or more). Further, if the display is in the nature of a cathode ray tube (CRT), then power at a much higher level (i.e., in excess of 10 kV) may be required.
In designing power supplies for systems such as personal computers, a designer may be required to consider a number of factors in achieving an efficient design. For example, if the designer were to specify a number of power supplies, each powered from an alternating current (AC) source, then the designer may be required to provide a step-down transformer for each supply and current protection of both sides of the power supply.
To avoid a multiplicity of power supplies, a designer will often select a voltage most heavily used within the system and design a power supply system around the one voltage. Where some devices require a higher voltage at a much lower power level, the designer may provide a step-up DC to DC converter to supply the specific device involved. Likewise, where a lower voltage is needed, the designer may provide a step-down DC to DC converter.
While DC to DC converters may be designed using a number of strategies, DC to DC converters usually require an internal oscillator. In the case of a step-up DC to DC converter, the oscillator is needed to chop an input DC supply signal into AC for application to a step-up transformer. The step-up transformer will, in turn, usually be followed by a rectifier and filter to provide the final desired voltage.
A step-down DC to DC converter will also often use a oscillator, but for a different reason. For example, if a step down converter were to use a step-down resistor or transistor to step the voltage down to an acceptable level, then a considerable amount of power would be dissipated in the resistor or transistor based upon the well known formula P=IV.
To avoid the heat dissipation in such step-down devices, a transistor connected to an oscillator will often be used to chop the input waveform into a series of pulses, where the width of each pulse is determined by the power required, using a technique called pulse width modulation (PWM). A rectifier may be used to rectify the chopped waveform into the final desired voltage.
The oscillator used in prior art step-up and step-down voltage converters is typically of a free-running variety operating at a constant frequency. Often the frequency is chosen in an effort to maximize transformer efficiency and to avoid transformer core saturation. In the use of PWM technology, the frequency is usually chosen to maximize the efficiency of the chopping and filtering devices.
Prior art voltage converters are known to suffer from poor efficiency. A free-running oscillator consumes a relatively constant level of power from no load to full load. Transformers inherently draw a magnetization current even under no-load conditions.
While prior art power supplies made of discrete components have been relatively effective, changing technology has rendered such devices difficult to use and relatively inefficient. For example, multifunction chips (e.g., application specific integrated circuits (ASICs) used in communications devices such as telephones, modems, video games, etc.) may require a number of different data processing technologies and internal voltages for proper operation. A microprocessor may require a 3.3 volt power supply, while a radio frequency (RF) transceiver may require 5 volts. An output power amplifier may require 12 volts, while a flat panel display may require as much as 17 volts.
Further, the more functions that are placed on a multifunction chip, the more chip leads are required for connection to the outside world to access and control those functions. The presence of multiple voltage requirements exacerbates the problem of accessability in that more leads must be dedicated to supplying those voltages to the internal structures requiring those voltages. Accordingly, a need exists for a structure for adjusting voltage levels within the chip that can be fabricated on the chip using known chip fabricating techniques.